<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .big {
            display: flex;
            flex-direction: row;
            /*盒子居左排*/
            flex-wrap: wrap;
            /*超过宽度换行*/
            flex-flow: row wrap;
            /*代替上面2个属性*/
            justify-content: center;
            /*水平居中对齐*/
            align-items: center;
            /*垂直居中对齐*/
        }
        .item {
                width: 200px;
                height: 200px;
                background-color: gray;
                margin: 0 10px;
                font-size: 64px;
            }
    </style>
</head>

<body>
    <div style="width: 100%; height:650px;background-color: red;" class="big">
        <div class="item" style="flex-grow:1">A</div>
        <div class="item" style="flex-grow:1">B</div>
        <div class="item" style="flex-grow:1">D</div>
        <div class="item" style="flex-grow:1">E</div>
        <div class="item">C</div>
    </div>
</body>

</html>